Tiacumicin B belongs to the family of Tiacumicins; Tiacumicins, produced by fermentation of Dactylosporangium aurantiacum, are a group of unsaturated 18-membered macrocyclic of the macrolide class that differs in the type of substituents of the unsaturated ring. Tiacumicin B has the structure shown below:

Tiacumicins and in particular Tiacumicin B show activity against a variety of bacterial pathogens including Clostridium difficile. 
The API crystallization process and crystal properties have a significant effect on downstream processing and formulation. Physical properties such as particle size, crystal habit, and surface properties are important aspects of API product quality and must be considered with great care and attention during the development of an API crystallization process.
For example, for insoluble or dissolution-limited drug substances, small particle size is necessary to maximize surface area to enhance bioavailability.
For development of drug product processes, particle uniformity may be critical to the homogeneity of a blend or granulation, which directly correlates with the content uniformity and dissolution properties of the drug product. In addition, API crystal properties, such as particle size distribution, habit, and surface properties, have a large effect on bulk powder properties, which may affect formulation operations such as blending, granulation, and compaction. Therefore, having consistent and optimal physical properties of the API is essential for development of formulation processes to produce consistent and reliable drug products.
There are several patents claiming different crystal forms of Tiacumicin B (U.S. Pat. No. 7,378,508, US 2013/0303472). The different polymorphic forms have the drawback to be fragile yielding a final API with a high amount of fine particles that makes the product difficult to formulate.
The control objectives for batch crystallization processes can be defined in terms of product purity, crystal habit, morphology, average particle size, crystal size distribution, bulk density, product filterability, and dry solid flow properties. It is known that the size, shape, and solid-state phase of the product crystals are dependent from the crystallization process.
The procedures described in the prior art suffer both for some drawbacks; U.S. Pat. No. 3,978,211 discloses a crystallization procedure yielding a well defined polymorph but an acicular shape and fragile crystals. In addition, the crystals obtained have a high amount of fine that make the product difficult to formulate. U.S. Pat. No. 7,378,508 discloses a procedure which requires about 3 to about 14 days, therefore not suitable for industrial application. In patent application US 2013/0303472, more suitable procedures are described, which on the other hand require high stressed drying conditions.
There is still a need to find a new crystal habit with improved hardness that can be easily formulated. Here will be disclosed a new crystal habit for Tiacumicin B and a new process for obtaining it.